1. Field of the Invention
This invention relates to a tilt type steering apparatus which adjusts the height position of a steering wheel for steering an automobile.
2. Related Background Art
An apparatus for adjusting the height of a steering wheel which is called a tilt type steering apparatus so as to be capable of changing the height of the steering wheel in conformity with a driver's constitution, driving posture or the like is known as described, for example, in Japanese Laid-Open Utility Model Application No. 5-22253. FIGS. 14-16 of the accompanying drawings show an example of a tilt type steering apparatus of which a part of the basic structure is similar to that described in the aforementioned publication and which has heretofore been widely used.
A steering shaft 1 is rotated by the operation of a steering wheel (not shown) fixed to the rear end portion (the right end portion as viewed in FIG. 14) thereof. This steering shaft 1 is inserted in a cylindrical steering column 2 and is supported inside the steering column 2 for rotation only. The fore end portion (the left end portion as viewed in FIGS. 14 and 15) of the steering column 2 is supported for pivotal movement relative to a vehicle body by a lateral shaft, not shown. Also, that portion of the intermediate portion of the steering column 2 which is near the upper end is supported on the vehicle body for adjustment in its vertical position.
A vertical position adjusting mechanism for this purpose is comprised of a fixed bracket 3 fixed to the vehicle body under a dashboard, and a vertically movable bracket 4 welded and fixed to the underside of the steering column 2. The fixed bracket 3 has a pair of left and right fixed plate portions 5 and 5 each disposed in a vertical direction. The steering column 2 is fixed to the vehicle body with that portion of the intermediate portion thereof which is near the upper end sandwiched between the two fixed plate portions 5 and 5 from the widthwisely left and right sides. The lower end edges of the fixed plate portions 5 and 5 are connected together by a connecting plate portion 13. Arcuate slots 6 and 6 centering around the above-mentioned lateral shaft are formed in the fixed plate portions 5 and 5 in a vertical direction.
On the other hand, the vertically movable bracket 4 is formed by bending a metallic plate having sufficient rigidity substantially into a C-shape, and is welded and fixed to the underside of that portion of the intermediate portion of the steering column 2 which is near the upper end and which is sandwiched between the pair of fixed plate portions 5 and 5. This vertically movable bracket 4 is formed with a pair of left and right circular holes 7 and 7 concentric with each other. A tilt bolt 8 is inserted in these circular holes 7, 7 and the above-mentioned slots 6, 6. A head 9 formed on one end portion (the right end portion as viewed in FIG. 16) of the tilt bolt 8 is engaged with one (the right one as viewed in FIG. 16) of the pair of slots 6 and 6 only for displacement in the lengthwise direction of said one slot 6 (the vertical direction as viewed in FIG. 16) (against rotation). Also, a tilt nut 10 is threadably engaged with that tip end portion of the tilt bolt 8 which protrudes from the outer side of the fixed plate portion 5 through the other (left as viewed in FIG. 16) slot 6.
Further, the base end portion of a tilt lever 11 is fixed to the tilt nut 10 by a fixing screw 12, and the tilt nut 10 is rotatable by the operation of the tilt lever 11. The spacing between the inner end surface of the tilt nut 10 and the inner side of the head 9 is adjustable on the basis of the rotation of the tilt nut 10. When the spacing between the inner end surface and the inner side is narrowed, the tilt nut 10 and the head 9 urge the inner sides of the pair of fixed plate portions 5 and 5 constituting the fixed bracket 3 against the outer side of the vertically movable bracket 4.
When the height position of the steering wheel is to be adjusted in conformity with the driver's constitution or the like by the prior-art tile type steering apparatus constructed as described above, the tilt lever 11 is operated to thereby loosen the tilt nut 10 and widen the spacing between the tilt nut 10 and the head 9. In this state, a frictional force created between the inner sides of the pair of fixed plate portions 5, 5 and the outer sides of the vertically movable bracket 4 becomes small. With this state kept, the tilt bolt 8 is moved along the slots 6, 6 in the fixed bracket 3 and the rear end portion of the steering column 2 is vertically moved to thereby move the steering wheel to a desired height position. With the height position of the steering wheel moved to the desired position in this manner, the tilt nut 10 is fastened by the tilt lever 11. As a result of this fastening, the spacing between the head 9 and the tilt nut 10 narrows and the inner sides of the pair of fixed plate portions 5 and 5 are strongly urged against the outer side of the vertically movable bracket 4, and a frictional force created between these surfaces becomes great. As a result, the upper portion of the steering column 2 is fixed at the position after adjusted.
It is desired that the prior-art tilt type steering apparatus constructed and acting as described above be improved in the following points (1) and (2):
(1) To improve the support rigidity of the steering column 2 relative to the fixed bracket 3; and
(2) To make the height H of the vertical position adjusting mechanism small.
Item (1) above is necessary to prevent the steering column 2 from vibrating during running or the like, and to prevent the steering wheel from being displaced (improve the feeling of support rigidity of the steering wheel) when a great load in a horizontal direction is applied to the steering wheel. Item (2) above is necessary to decrease the amount of protrusion of the vertical position adjusting mechanism from the underside of the dashboard and prevent the driver's knees or the like from interfering with the vertical position adjusting mechanism.
To satisfy the requirement of item (1) above, it is effective not to hold down the vertically movable bracket 4 fixed to the underside of the steering column 2, but to hold down the steering column 2 from both sides, when fixing the height position of the steering wheel. However, any practical structure for holding down the steering column 2 in this manner is not yet known. Japanese Laid-Open Utility Model Application No. 55-121771 describes a structure in which click mechanisms each provided with a compression spring, a ball and a depression are provided on the left and right sides of a steering column and the left and right sides of the steering column are supported by the click mechanisms. However, the structure described in this publication is very special and moreover is not a structure which firmly holds down the steering column when the height position of the steering wheel is to be fixed. Accordingly, by the structure described in this publication, it is impossible to provide a practical structure and moreover improve the support rigidity.
Also, to satisfy the requirement of item (2) above, it would occur to mind to make the height of the fixed bracket 3 small. For this purpose, it is conceivable to eliminate the connecting plate portion 13 connecting the lower end edges of the pair of left and right fixed plate portions 5 and 5 constituting the fixed bracket 3, and this is partly practised. By such a method, the height H of the vertical position adjusting mechanism can be made more or less small, but a sufficient effect cannot always be obtained. On the basis of the presence of the vertically movable bracket 4 fixed to the underside of the steering column 2, the shortening of the height H is limited. That is, the fixed plate portions 5 and 5 must be capable of sandwiching the vertically movable bracket 4 from both sides even in a state in which the steering wheel has been most lowered. Therefore, the lower end position of these fixed plate portions 5 and 5 must be low to a certain degree. Moreover, this lower end position remains unchanged even When the vertically movable bracket 4 is moved up to make the position of the steering wheel high, and the lower end position does not rise even when a driver of large build drives with the position of the steering wheel heightened. Therefore, when a driver of large build drives, his or her knees become ready to interfere with a cover (not shown) covering the vertical position adjusting mechanism. The reduction in support rigidity by the elimination of the connecting plate portion 13 cannot be neglected in some cases.